Princeton university reported data from a study where they hired experimental confederates (people) to attend speed dating events, posing as daters, and carefully take notes on the behaviors of the daters. what type of research design did they use?

Naturalistic observation

Explanation:

Naturalistic observation is a method of study that psychologists and many other researchers typically use.

This process includes the study in their natural setting of subjects.

It is often used in circumstances where  performing laboratory research is impractical, costly, or would have an adverse effect on the actions of the subject.